Unlock Specialist Mode:
This feature becomes unlocked when you complete the game once on any difficulty setting.
Unlock YOLO Mode:
This feature will become unlocked when you have successfully completed the campaign on the Specialist difficulty setting. In YOLO mode you will die just as quickly as you do on the highest difficulty setting, but when you die for the first time you will start the game from the beginning. You cannot reload checkpoints or restart after death but you are able to pause, save and exit the game and return and play it again later from that point.